1. Field of the Invention
The present invention relates to a vacuum container or vacuum envelope and a display device where a vacuum state is maintained by spreading getter materials in a vacuum casing such as a vacuum envelope or enclosure. Characteristic examples of such a display device are a vacuum-type video display with electron emitter elements such as a field emission display (referred to as “FED” hereinafter), a vacuum fluorescent display (VFD), and a field emission (FE) sensor.
2. Description of the Prior Art
As liquid crystal displays have commonly been used as flat-panel displays, they may be replaced by FEDs.
FIG. 11 is a cross sectional view of a conventional FED with electron emitter elements. The FED has a vacuum envelope 18 composed of an electron emission substrate 25 and a light emitter substrate 26 where the two substrates 25 and 26 are air-tightly joined to each other by a spacer 3. The electron emission substrate 25 is provided thereon with a pattern of wiring layer 12, electron emitter elements 13, a pattern of insulating layer 14, and lead electrodes 15, and the light emitter substrate 26 is provided thereon with an opposite pattern of anode layers 16 and a pattern of fluorescent layers 17. A getter chamber 20 of a box-like shape is provided on the back side of the electron emitter substrate 25 of the vacuum envelope 18. The getter chamber 20 is communicated via an exhaust aperture 23 with the interior of the vacuum envelope 18 and the getter chamber 20 includes a getter 4 held under pressure by a spring 21.
The getter 4, as shown in FIG. 12, comprises a getter material 6 filled in an annular, nickel plated metallic frame 5 for gettering action. The getter material 6 may be a powder alloy of, for example, BaAl4. In process, the air in the vacuum envelope 18 and the getter chamber 20 is discharged out through from the exhaust aperture 24 of the getter chamber 20 and an exhaust tube 22. Then, when the exhaust tube 22 has been sealed, the vacuum envelope 18 and the getter chamber 20 are turned to and maintained in a vacuum state. As the getter 4 is heated by means of such as a high-frequency induction heating method (not shown), the getter material 6 is vapor deposited on an inner surface portion of the getter chamber 20 to form a getter film 19. The vacuum state in the vacuum envelope 18 and the getter chamber 20 is maintained in a higher degree of vacuum, so that the emission of electrons from the electron emitter elements 13 can stably be carried out.
It is essential for the display device having the above described arrangement to maintain the vacuum state to such a higher degree of vacuum in the vacuum envelope that electrons can steadily be emitted at high efficiency and lower currents. For increasing the vacuum state to a high degree of vacuum, the effect of the getter absorbing gases is utilized. However, since the getter is directly supported by the spring 21 in the vacuum envelope, the getter material can hardly be controlled for spreading while being heated and vaporized by high-frequency heating. As a result, undesired conductive regions will be developed in the vacuum envelope. For eliminating the drawback, the getter chamber is located beneath the vacuum envelope but such a location thus may interrupt the flat-panel configuration of the display device. Note here that the undesired conductive regions are developed by portions of the getter material spread and deposited on a display area thus to establish undesired connection between the electrodes which are not to be electrically connected.